1. Field of the Invention
The present invention relates to an electrostatic discharge protection circuit, and more particularly, to an electrostatic discharge protection circuit with adjustable time constant.
2. Description of the Prior Art
In recent years, because the request of law of electrostatic discharge (ESD) of electronic product are gradually increasing, except the ESD test on component level, the ESD gun test, the electrical fast transient (EFT) test, and the surge test on system level are also added into the product verification item gradually. However, the ESD stress duration of each kind of ESD test is different, for example, the ESD stress duration of the ESD gun test and the surge test on system level both are longer than that of the ESD test on component level. Therefore, how to design the ESD protection circuit in response to different tests and different products to make the ESD protection circuit can drain out the ESD current effectively in different situations to achieve the effect of protecting internal circuit is an important issue.